1979 年 11 巻 1 号 p. 19-38_2
Fledged family life
Nest-leaving: Behaviors of chicks and parents at nest-leaving of chicks are summarized as follows
Feeling near flying of chicks from nest, the female utters her soft nasal nga-notes addressing to chicks, lengthens the feeding intervals so as to invoke the nest-leaving mood of chicks by causing the restless irritation from increasing hunger. The male chiefly watches her, feeding the chicks with still longer intervals.
From a few days before nest-leaving, the chicks stand on nest-wall, preening (taking off descamating sheath of growing feathers), stretching and with jumping or wing flapping excercise, and finally they leave the nest to perch on near branches. Then they gradually move to upward branches to roost there for the night.
This is usually toward evening and the root of such nest-leaving behavior may be in correlation with inherent roosting drive.
Having once left the nest, the chicks would not come back to, or roost, on the nest (although they may temporarily perch on it while moving through the branches).
During the day, the fledged chicks sit still in the foliage, sleeping and waiting the parents for food. The feeding frequency by parents 4 days after chicks' flying was 1.3 times per hour.
On the 3rd day after fledged, a chick could fly about 30m and on the 8th day they flew 40-50m and came back to their perch.
At the first night of fledging from nest, the chicks roosted on perches where they sat during the day and parents took roost (both in 1969 and '70, though they flew off to "flock roost" in 1977) below the nest-tree ("nest-site roost"), as if to guard the chicks (which are sleeping above in the tree, keeping individual distance of several meters. This may have an effect of distrupting the predator's attention. Thereafter, the parents roosted either in "nest-site", "territory" roost or flew off to "flock roost", reacting to the condition of chicks (If fed enough the chicks roosted quietly but if not they were irritated by hunger and in this case parents' (female) reaction involved some judgment behavior (cf. Kuroda 1969).
The period of fledged family life can be summarized by dividing four periods:
1. First period from fledging to 4th or 5th day.
The chicks rest and wait parents' feeding perched in nest-tree (or adjacent taller tree) where they roost at night. The parents may roost below in "nest-site roost" (guarding chicks) or in "territory roost", or flly off to "flock roost" (judging the condition of the chicks).
2. Five to ten days after fledged.
The chicks begin to fly around the nest-tree, and the parents guide them (one chick after another by repeated trips to and from the roost-site and chick) to "nest-site" roost to sleep there by family.
3. Ten to twenty days after fledged.
Fledged family accompanied by female may move around for food chiefly within 100m from the nest-tree. But, usually a delayed chick remains in the nest-tree a few more days. Parents may guide chicks to "territory roost" to roost by family. Territory defense of parents are weakened and their chick guard drive reaches to its peak. The begging voice of chicks get lauder.
4. After twenty days from fledging.
At about 20 days from fledging the young (now to be so called) may be guided by parents to "flock roost" about 1km apart. From this day, well grown young may join to young crow group of the "flock roost" area, and may not return to parents' territory. But, a delayed young, having guided by parents to "flock roost" a few days after well grown mates, would return to parents' territory by itself (possibly urged to do so by "loneliness".).
Such a family life of parents and a delayed young may continue 50-100 days, during which the parents would never reject the young from their territory. But, the latter gradually behaves independent of parents, not returning to territory on some days, and finally deserts the territory.